The present invention relates to a control apparatus and a method for an internal combustion engine.
When an internal combustion engine such as an engine for an automobile is stopped in a normal operation, fuel injection and ignition in the internal combustion engine are stopped as a driver turns off the ignition switch. As a result, the engine rotation speed is gradually reduced by the rotational resistance caused by, for example, the pressure in each combustion chamber during a compression stroke. After the internal combustion engine rotates in reverse once by the pressure in the combustion chambers, the engine rotation finally stops.
However, if the internal combustion engine is stopped before achieving fully autonomous operation because of an operational error of the ignition switch while the engine is being started, or if the engine is stopped by a stall during operation, that is, when the internal combustion engine is stopped because of abnormality, fuel injection and ignition are continued in order to achieve autonomous operation while the rotation speed is reduced during an engine stopping process. Therefore, fuel injection and ignition are performed during reverse rotation of the engine in the engine stopping process. This could lead to failure of the internal combustion engine due to combustion of fuel in a reverse rotation state.
To avoid such a problem, ignition of the engine is prohibited when the engine rotation speed is reduced to a level (for example, 200 rpm) that could stop the engine rotation during operation of the internal combustion engine. In this case, during the stopping process performed when the internal combustion engine is stopped because of abnormality, ignition is prohibited when the engine rotation speed becomes less than the above mentioned level. Therefore, ignition is not performed during reverse rotation of the internal combustion engine in the stopping process, and combustion of fuel in the reverse rotation state is avoided.
During cranking or autonomous operation of the internal combustion engine, even if the engine rotation speed is reduced to below the above mentioned level for some reason, ignition is preferably continued to achieve autonomous operation from that point until reverse rotation is caused. However, when the ignition is prohibited, the possibility of achieving autonomous operation of the internal combustion engine is eliminated due to the prohibition of ignition during the period from when the engine rotation speed is reduced to below the above mentioned level until reverse rotation is performed. That is, ignition is prohibited more than necessary.
Also, if reverse rotation of the internal combustion engine is detected, ignition can be suppressed from being prohibited more than necessary as described above by prohibiting ignition only when the internal combustion engine rotates in reverse. Therefore, it has been proposed that reverse rotation of the engine be detected using a crank signal or a cam signal of the internal combustion engine.
The crank signal is a signal used for, for example, detecting the crank angle of the internal combustion engine, and is output from a crank position sensor in the vicinity of a crank rotor attached to the crankshaft in accordance with rotation of the crankshaft at, for example, every 10° of crank angle. That is, the shape of the crank rotor is designed such that the crank signal is output from the crank position sensor at equal intervals.
Meanwhile, the cam signal is used for distinguishing cylinders of the internal combustion engine, and is output from a cam position sensor in the vicinity of a cam rotor attached to the camshaft at unequal intervals with respect to constant rotation of the camshaft. That is, the shape of the cam rotor is designed such that the cam signal is output in such a manner from the cam position sensor. The cylinders of the internal combustion engine are distinguished based on the cam signal and the crank signal. The output intervals of the cam signal are normally set longer than the output intervals of the crank signal. This is because the cam signal is used only for distinguishing the cylinders, and does not need to be output at a short interval such as 10° CA like the crank signal.
When the internal combustion engine is rotated in reverse, the output pattern of the crank signal output at equal intervals of every 10° of crank angle is not changed from that during forward rotation, but the output pattern of the cam signal output at unequal intervals becomes different from that during forward rotation. Therefore, the occurrence of reverse rotation of the engine is detected based on the change in the output pattern of the cam signal with respect to the crank signal due to reverse rotation of the internal combustion engine.
However, since the output intervals of the cam signal are relatively long as described above, it takes time for the influence of reverse rotation to appear in the output pattern of the cam signal from when the internal combustion engine is actually rotated in reverse. Therefore, by the time the occurrence of reverse rotation of the internal combustion engine is detected, reverse rotation may already be advanced and ignition in such a state may have been performed. To avoid such a circumstance, a cam rotor having a shape that shortens the output intervals of the cam signal may be used. However, in this case, an additional cam rotor needs to be prepared. This is inevitably troublesome and costly.
Instead of using the cam rotor having the above mentioned shape, the occurrence of reverse rotation of the internal combustion engine may be detected by applying a technique disclosed in Japanese Laid-Open Patent Publication No. 10-220330. In the above publication No. 10-220330, two crank position sensors are provided. The sensors are arranged such that the crank signals are alternately output from the two crank position sensors during forward rotation of the engine. Then, the occurrence of reverse rotation of the internal combustion engine is detected when the crank signals are output several times from one of the crank position sensors while the crank signal is output from the other crank position sensor. Therefore, by applying the technique of the above publication No. 10-220330, the occurrence of reverse rotation of the internal combustion engine is detected without changing the cam rotor with the one for detecting reverse rotation.
As described above, when the occurrence of reverse rotation of the internal combustion engine is detected by applying the technique of the above publication No. 10-220330, the occurrence of reverse rotation of the internal combustion engine is detected without changing the cam rotor with the one for detecting reverse rotation. However, two crank position sensors need to be provided to detect the occurrence of reverse rotation of the internal combustion engine. This causes trouble to provide an extra crank position sensor and increases in the costs.